The invention relates to intelligent networks and particularly to maintaining a connection between an intelligent network control point and a switching point when a subscriber roams.
In telecommunications networks intelligence is related to the ability to obtain stored data, to process it and to make decisions based thereon. Even the present telecommunications networks, such as public switched telephone networks PSTN, are to some extent intelligent since they are capable of processing stored data for example in call routing. A typical xe2x80x9cintelligentxe2x80x9d facility in the present telecommunications networks is the conditional call forwarding where the call situation must be analyzed and the call must be routed according to the stored service profile of the call forwarding. However, such intelligent facilities are an integral part of the basic network, wherefore changing or adding of facilities requires, for example, software updates in all exchanges of the network.
An Intelligent Network (IN) is a network architecture which is added to the basic network and which enables faster, easier and more flexible implementation and control of services. This is achieved when control of services is removed from the telephone exchange to a separate-functional unit in the intelligent network. The services thus become independent of the operation of the basic network, wherefore the structure and software of the basic network do not have to be changed when services are altered or added. An intelligent network may comprise several service providers in addition to the actual network operator.
In the last few years intelligent networks have been standardized to a greater and greater extent in fixed networks. These standards define a certain operational and hierarchic model for intelligent networks. In this model service control is transferred from a basic network exchange to a service control point (SCP) in the intelligent network. The SCP comprises the required database and service logic programs (SLP), i.e. computer programs implementing the logical structure of a particular service (service logic). Intelligent network IN services are developed and tested with particular equipment called service creation environment (SCEP). A service management function (SMF) controls data related to the users and the network in a database, including service-specific data and service programs. A service switching point (SSP) is an exchange, for example an exchange in the basic network, which implements a service switching function (SSF), i.e. it identifies the IN service and activates interworking with the SCP. When a call with an IN service is set up, the SSP manages the connection arrangements. The IN service is provided such that when the SSP encounters service-related detection points it requests for instructions from the SCP. In other words, the SSP gives control to the SCP and starts waiting for operations from the SCP. When an IN service is triggered, a service logic program SLP is activated in the SCP and it determines the instructions the SCP transmits in each call phase to the SSP. The SSP interprets the instructions and starts the call control functions they require. Triggering of an IN service means that an IN function is activated due to an impulse occurring when a certain detection prerequisite is fulfilled.
As described above, the IN standards are developed for fixed telecommunication networks. It is difficult to implement IN functionality in a mobile network where mobile subscribers have no fixed access point in the network. However, it is necessary that for example mobile subscribers using IN services can be identified and data about the services of each subscriber can be found everywhere in the mobile network. This easily leads to massive databases and/or a need to transmit a great deal of data within the mobile network.
For example in a GSM (Global System for Mobile Communication) system a connection to an intelligent network service control point SCP is maintained such that as the subscriber roams from the area of a mobile services switching centre (MSC) operating as the IN SSP to the area of another MSC, the original centre acts as the controlling anchor MSC, to which data about events in the new MSC is transmitted by means of the MAP protocol. The connection to the IN SCP can thus remain in the original MSC. Instead, for example in a GPRS (General Packet Radio Service) system there is no anchor node corresponding to an anchor MSC, but the control of the packet-switched connection is transferred as the subscriber moves from the area of a support node (Serving GPRS Support Node, SGSN) operating as the IN SSP to the area of another support node. This means that the connection to the IN SCP must be transferred from one support node to another. A problem in the above-described arrangement is how to maintain the states of the service logic programs of the IN SCP corresponding to the connection when the support node changes. Maintaining the states is essential in order that the original service logic program SLP is able to control the packet-switched connection smoothly even if the subscriber roams in the areas of different support nodes.
An object of the invention is to develop a method and an apparatus implementing the method such that the aforementioned problems can be solved. Specifically, the invention relates to a method of maintaining a connection between an intelligent network control point and a switching point in a telecommunications system comprising at least one subscriber and an intelligent network comprising service switching points and at least one service control point that contains service logic programs. The method is characterized by providing a service connection with an identifier when a service connection is set up between an intelligent network control point and a first switching point or when the intelligent network switching point used in the service connection changes, transmitting the service connection identifier and preferably the address of the control point and the state data of the switching point corresponding to the service connection from the old switching point to the new switching point whenever the subscriber moves from the area of one switching point to the area of another switching point, and setting up a service connection by means of the transmitted data from the new switching point to the control point, whereafter the service logic program to be used, corresponding to the service connection, is identified by means of the service connection identifier.
The invention is based on the idea of providing a service connection in an intelligent network with an identifier that links the service logic program of the IN control point and the corresponding service connection. The service connection identifier can be formed either in the switching point or in the control point of the intelligent network. The service connection identifier is any identifier which identifies a particular service logic instance in a specified service control point. The service logic instance is an embodiment of a service logic program in the execution. In the following, a xe2x80x98service logic programxe2x80x99 refers to a service logic instance. The service connection identifier is formed either when the service connection is set up or, alternatively, the identifier is obtained from the IN control point after it has been informed of a change in the switching point. A service connection is set up between an intelligent network switching point and a control point after an IN service has been triggered or when the service control function requests the switching point to activate an event (e.g. a call). The service connection enables the transmission of operations of the intelligent network application protocol (INAP) between the service control function and the switching point of the intelligent network. One service connection is connected to one active event in the switching point, such as a call or a packet data connection (GPRS MM context or PDP context), or to several events that are logically related, for example associated with the same subscriber. If there is a change in the switching point from which the service connection to the control point is set up, in which case the service connection is re-established from a new switching point to the control point, the new connection can be guided by means of the identifier to use the original service logic program.
An advantage of the method according to the invention is that the service logic programs maintain their states, and therefore the same service logic program is able to monitor the entire service connection from the beginning to the end even if the connection had to be re-established every now and then from a new switching point as a result of a change in the switching point.
The invention also relates to a telecommunications system comprising at least one subscriber and an intelligent network comprising service switching points and at least one service control point comprising service logic programs. The system is characterized in that it is arranged to provide a service connection with an identifier when a service connection is set up between an intelligent network service control point and a first switching point or when the intelligent network switching point used for the service connection changes, to transmit the service connection identifier and preferably the address of the control point and the state data of the switching point corresponding to the service connection from the old switching point to the new switching point whenever the subscriber moves from the area of one switching point to the area of another switching point, and to set up a service connection by means of the transmitted data from the new switching point to the control point, whereafter the service logic program to be used, corresponding to the service connection, is identified by means of the service connection identifier. With such a system the advantages provided by the method according to the invention can be achieved in a simple manner.